Git rebase and Git merge are two fundamental commands used for managing repository history in Git version control systems. Rebase re-sequences commits on top of a target branch, rewriting the commit history and creating new commit IDs, while merge joins two or more development histories together without rewriting commits. The choice between rebase and merge depends on the specific use case, such as when to synchronize a feature branch with the main branch, update a public branch, or squash intermediate commits. While both commands have their benefits and pitfalls, rebase offers streamlined commit history and the possibility to truncate unnecessary commits, but also requires caution when used on public branches due to potential rewriting of commit history and force push requirements.